In general, this project proposes the use of missense suppression as a means of obtaining tRNAs with mutationally altered functions and interactions. It calls for the utilization of mutations involving known codon changes at one position of the tryptophan synthetase alpha subunit, and knowledge of the behavior of (virtually) all amino acids at that position in the protein, to obtain the conversion of specific tRNAs to new coding and amino acid accepting specificities. It aims at the preliminary characterization, isolation and purification of the altered tRNAs by column chromatography, determination of the changes in nucleotide sequence and/or extent of base modification, and correlation of altered sequence with altered functions and other changes in tRNA structure and molecular interactions.